The present invention relates to a laser beam survey instrument, in which a laser beam can be projected at an arbitrary tilt angle to a horizontal plane.
Among conventional type laser survey instruments, there may be mentioned instruments which form a horizontal reference line by projecting a laser beam in a horizontal direction, instruments which form a horizontal reference plane by scanning a laser beam in a horizontal plane or by spreading a laser beam in a plane by means of a conical prism.
Among such laser survey instruments, there has been proposed an instrument, which comprises a tilt detector integrally fixed with a laser projector, and the laser projector is titled according to signal from the tilt detector, and it is designed that the laser beam is always directed horizontally even when the laser survey instrument is installed at a tilted position.
Also, there has been proposed an instrument, in which a laser beam is not only projected in a horizontal direction but also can be projected at a desired tilt angle with the horizontal plane as a reference.
When it is desired to tilt the laser beam from the laser projector at an arbitrary angle in the conventional type of laser survey instrument, the tilt detector is first tilted at a desired angle to the laser projector. Then, the laser projector is tilted so that the tilt detector is at the horizontal position, and the laser beam is projected at a desired tilt angle.
As described above, in the conventional type of laser survey instrument, the tilt detector is tilted with respect to the laser projector each time the reference plane is set at an arbitrary angle. As a result, if there is an error in the tilt drive unit of the tilt detector, positioning deviation occurs in each setting operation. Therefore, if the tilt detector with positioning deviation is taken as a reference, optical axis tilt error of the laser projector occurs. If the reference line or reference plane is formed by the laser beam, a setting error occurs. There is no way of correcting the positioning deviation. If errors are accumulated at each setting, the errors on the reference plane may reach an unallowable value.
Thus, in order to minimize the positioning deviation, a mechanical unit must be provided, which produces less error and high reproducibility in the conventional system; however, this leads to an increase in cost of production.
To solve the above problems, it is an object of the present invention to provide a laser survey instrument, in which no positioning deviation occurs between the tilt detector and the optical axis of the laser projector, and if positioning deviation does occur, it can be easily corrected.